Vertical packaging for ultrasound-on-a-chip and related methods

ABSTRACT

Vertical packaging configurations for ultrasound chips are described. Vertical packaging may involve use of integrated interconnects other than wires for wire bonding. Examples of such integrated interconnects include edge-contact vias, through silicon vias and conductive pillars. Edge-contact vias are vias defined in a trench formed in the ultrasound chip. Multiple vias may be provided for each trench, thus increasing the density of vias. Such vias enable electric access to the ultrasound transducers. Through silicon vias are formed through the silicon handle and provide access from the bottom surface of the ultrasound chip. Conductive pillars, including copper pillars, are disposed around the perimeter of an ultrasound chip and provide access to the ultrasound transducers from the top surface of the chip. Use of these types of packaging techniques can enable a substantial reduction in the dimensions of an ultrasound device.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation claiming the benefit under 35 U.S.C.§ 120 of U.S. application Ser. No. 16/401,249, filed May 2, 2019, andentitled “VERTICAL PACKAGING FOR ULTRASOUND-ON-A-CHIP AND RELATEDMETHODS,” which is hereby incorporated herein by reference in itsentirety.

U.S. application Ser. No. 16/401,249 claims the benefit under 35 U.S.C.§ 119(e) of U.S. Provisional Patent Application Ser. No. 62/666,560,filed May 3, 2018, and entitled “VERTICAL PACKAGING FOR TRANSDUCER ONCMOS SENSOR,” which is hereby incorporated herein by reference in itsentirety.

BACKGROUND Field

The present application relates to micromachined ultrasound transducers.

Related Art

Some micromachined ultrasound transducers include a flexible membranesuspended above a substrate. A cavity is located between part of thesubstrate and the membrane, such that the combination of the substrate,cavity, and membrane form a variable capacitor. If actuated, themembrane may generate an ultrasound signal. In response to receiving anultrasound signal, the membrane may vibrate, resulting in an outputelectrical signal.

BRIEF SUMMARY

Some embodiments relate to an ultrasound device comprising anultrasound-on-a-chip having a first surface configured to be mounted toa substrate, the ultrasound-on-a-chip comprising an array of ultrasoundtransducers; and an integrated interconnect for electrically connectingthe substrate to at least one ultrasound transducer of the array ofultrasound transducers, at least a portion of the integratedinterconnect extending in a direction angled with respect to the firstsurface.

In some embodiments, the ultrasound-on-a-chip comprises a trench and theintegrated interconnect comprises one or more vias formed in the trench.

In some embodiments, at least a portion of the trench is lined with aninsulative material.

In some embodiments, the integrated interconnect further comprises aconductive layer disposed over the insulative material.

In some embodiments, the ultrasound device further comprises a bond padformed on the first surface of the ultrasound-on-a-chip and inelectrical communication with at least one via of the one or more vias.

In some embodiments, the trench is formed through the first surface.

In some embodiments, the at least one ultrasound transducer of the arrayof ultrasound transducers comprises an electrode proximate the firstsurface and in electrical connection with a first via of the one or morevias; a membrane proximate a second surface of the ultrasound-on-a-chipopposite the first surface, the membrane being in electrical connectionwith a second via of the one or more vias; and a cavity formed betweenthe electrode and the membrane.

In some embodiments, the integrated interconnect comprises a conductivepillar and a conductive layer electrically connecting the conductivepillar to the at least one ultrasound transducer.

In some embodiments, the ultrasound-on-a-chip comprises a second surfaceopposite the first surface, the conductive layer being adjacent thesecond surface.

In some embodiments, the conductive pillar extends in a directionsubstantially perpendicular to the first surface and the conductivelayer extends in a direction substantially parallel to the firstsurface.

In some embodiments, the conductive pillar is embedded in a supportcomprising an insulative material.

In some embodiments, the integrated interconnect comprises athrough-silicon-via (TSV) adjacent the first surface of theultrasound-on-a-chip.

Some embodiments relate to an ultrasound device comprising a packagehaving a width along a first direction that is less than 30 mm. Thepackage comprises an ultrasound-on-a-chip comprising an array ofultrasound transducers; and an interposer spaced from theultrasound-on-a-chip in a second direction perpendicular to the firstdirection.

In some embodiments, the ultrasound-on-a-chip comprises a trench and oneor more vias formed in the trench, the one or more vias electricallycoupling the interposer with the array of ultrasound transducers.

In some embodiments, the package further comprises:

a conductive pillar attached to the interposer and a conductive traceelectrically connecting the conductive pillar to at least one ultrasoundtransducer of the array of ultrasound transducers.

In some embodiments, the ultrasound-on-a-chip comprises athrough-silicon-via (TSV) electrically coupled to the interposer.

Some embodiments relate to an ultrasound device comprising a substrate;an ultrasound-on-a-chip disposed on the substrate and comprising anarray of ultrasound transducers; and means for electrically connectingthe array of ultrasound transducers to the substrate.

In some embodiments, the means comprises one or more vias integrated inthe ultrasound-on-a-chip.

In some embodiments, the ultrasound-on-a-chip comprises a trench and theone or more vias are formed in the trench.

In some embodiments, the means comprises a conductive pillar attached tothe substrate and a conductive trace electrically connecting theconductive pillar to at least one ultrasound transducer of the array ofultrasound transducers.

BRIEF DESCRIPTION OF DRAWINGS

Various aspects and embodiments of the application will be describedwith reference to the following figures. It should be appreciated thatthe figures are not necessarily drawn to scale. Items appearing inmultiple figures are indicated by the same reference number in all thefigures in which they appear.

FIG. 1A is a schematic diagram of an ultrasound device including wires,according to some embodiments of the present application.

FIG. 1B is a schematic diagram of an ultrasound device includingvertical integrated interconnects, according to some non-limitingembodiments of the present application.

FIG. 2A is a cross-sectional view of an ultrasound chip including anedge-contact via, according to some non-limiting embodiments of thepresent application.

FIG. 2B is bottom view of the ultrasound chip of FIG. 2A, according tosome non-limiting embodiments of the present application.

FIGS. 3A-3F illustrate a fabrication sequence for forming the edgeconnect via of FIG. 2A, according to some non-limiting embodiments ofthe present application.

FIG. 4 is a cross sectional view of an ultrasound chip includingedge-contact vias during packaging, according to some non-limitingembodiments of the present application.

FIG. 5 is a cross sectional view of an ultrasound chip including throughsilicon vias, according to some non-limiting embodiments of the presentapplication.

FIG. 6 is a cross sectional view of an ultrasound chip including throughsilicon vias during packaging, according to some non-limitingembodiments of the present application.

FIGS. 7A-7F illustrate a fabrication sequence for forming the ultrasoundchip of FIG. 5, according to some non-limiting embodiments of thepresent application.

FIG. 8 is a cross sectional view of an ultrasound chip includingconductive pillars, according to some non-limiting embodiments of thepresent application.

DETAILED DESCRIPTION

Conventional ultrasound systems are large, complex and expensive, andare typically only purchased by large medical facilities withsignificant financial resources. Recently, less expensive, portable, andless complex ultrasound imaging devices have been introduced. Suchimaging devices include ultrasonic transducers monolithically integratedonto a single semiconductor ultrasound-on-a-chip to form a monolithicultrasound device. Being monolithic, these devices are substantiallymore compact than conventional ultrasound systems.

Applicant has appreciated, however, that an additional reduction in thesize of these monolithic ultrasound devices may be beneficial. Certaindiagnoses that rely on ultrasound imaging require the ability to probesmall anatomical features, such as the interstices that separateadjacent ribs of a patient. Small probe heads are needed to probe suchsmall features. Applicant has appreciated that some probe heads thatimplement ultrasounds-on-a-chip are still too large to enable probing ofsuch small anatomical features. Applicant has further appreciated thatthe relatively large size of these probe heads results from the use ofwire bonding with the chip package. The relatively large size of theseultrasound chips stems from the fact that wire bonding involves the useof electrical connections that are not integrated as part of the chip.More specifically, wire bonding involves the use of discrete wires thatplace individual ultrasound transducers in electrical communication withthe respective control circuits. Dedicated machines designed to attachthe ends of a wire to the desired locations are used to perform wirebonding. Collectively, these wires can occupy more volume inside thepackage than the chip itself, thus posing a limit to the minimumdimension of the package.

Applicant has further appreciated that ultrasound chips including bondwires are power hungry, which may render these devices unsuitable foruse in low-power applications and/or may require complex coolingdevices. The relatively large power consumption results from the lengthof these wires, which, in turn, gives rise to large inductance. Suchwires, in fact, can be as long as 3 mm or more in some implementations.

Aspects of the present application are directed to ultrasound devicesthat use interconnects for placing the ultrasound transducers inelectrical communication with the control circuits that are integratedwith the ultrasound chips. Unlike wires used for wire bonding, theintegrated interconnects described herein can be made usingmicrofabrication techniques, and consequently, are embedded in theultrasound chip. Such interconnects may be substantially shorter thanbond wires. For example, such interconnects may be shorter than 1.5 mm,shorter than 1 mm, shorter than 0.5 mm, or shorter than 0.2 mm, amongother possible values.

Compared to wire bonding implementations, use of integratedinterconnects can result in a substantial reduction in the overall sizeof the package. This, it turn, can result in a more compact probe head.Furthermore, use of integrated interconnects can result in a substantialreduction in inductance, and as a result, in power consumption. Thus,the ultrasound devices described herein can be employed in applicationsrequiring small probe heads and/or in applications requiring low powerconsumption. Additionally, or alternatively, these ultrasound devicesmay reduce the complexity of the cooling system.

FIG. 1A illustrates a package including a wire bondedultrasound-on-a-chip and FIG. 1B illustrates a package including anultrasound-on-a-chip implementing integrated interconnects of the typesdescribed herein. Referring first to FIG. 1A, package 100 is designed tobe mounted on a printed circuit board (not shown in FIG. 1A), and theresulting assembly to be installed in an ultrasound probe head. Package100 includes un ultrasound-on-a-chip 102, an interposer 104 and wires108. Ultrasound-on-a-chip 102 includes ultrasound transducers foremitting ultrasound waves and/or detecting ultrasound waves. Interposer104 includes conductive traces for routing electrical signals betweenultrasound-on-a-chip 102 and the printed circuit board.

Ultrasound-on-a-chip 102 is placed in electric communication with theconductive traces of interposer 104 by wires 108, which are deployedusing wire bonding techniques. Because of the lateral extension of wires108, which can be as long as 3 mm or more in some implementations, thelateral extension of the overall package can be large, which may limitthe usefulness of the ultrasound probe head in which package 100 isdisposed. In some implementations, the width of the package may impactthe overall size of the ultrasound probe head, and as a result, theability to probe small anatomical features. As a result, theseultrasound probe heads may be unsuitable for certain types of diagnoses.The width w1 of the package may be greater than 5 mm, greater than 7.5mm, or greater than 1 cm.

Wire bonding packaging may be cumbersome in some implementations, as itmay require several steps for attaching the wires to the chip.Furthermore, wire bonded packages may exhibit mechanical stress.

FIG. 1B is a schematic diagram of a package including anultrasound-on-a-chip in which vertical packaging techniques are usedinstead of wire bonding, in accordance with some embodiments. Package120 includes ultrasound-on-a-chip 122 and interposer 124.Ultrasound-on-a-chip 122 is placed in electric communication withinterposer 124 by vertical integrated interconnects, examples of whichinclude edge-contact vias, conductive pillars and through silicon vias,as described in detail further below. As shown in this figure, theabsence of wires enables a substantial reduction in the width (w2) ofthe package. For example, in some embodiments, width w2 may be between 1mm and 50 mm, between 1 mm and 40 mm, between 1 mm and 35 mm, between 1mm and 30 mm, between 1 mm and 25 mm, between 1 mm and 20 mm, between 1mm and 15 mm, between 1 mm and 10 mm or between 1 mm and 5 mm, or anyother suitable range within such ranges. Other ranges are also possible.

In some embodiments, the relatively small size of package 120 may enableprobing of small anatomical features. Alternatively, or additionally,the relatively small size of package 120 may enable integration ofadditional acoustic structures (e.g., acoustic lenses) inside theultrasound probe head.

In some of the embodiments in which bonded wires are absent in package120, packaging of ultrasound-on-a-chip 122 may be substantially lesscumbersome than packing of ultrasound-on-a-chip 102. This is because thesteps required for attaching the wires may be omitted. Furthermore, theabsence of bonded wires may lead to the mechanical stress onultrasound-on-a-chip 122 may being substantially less than themechanical stress on ultrasound-on-a-chip 102.

Some embodiments are directed to means for electrically connecting anarray of ultrasound transducers of an ultrasound-on-a-chip to asubstrate (e.g., an interposer, a printed circuit board or any othertype of carrier) on which the ultrasound-on-a-chip is disposed. Suchmeans may comprise one or more edge-contact vias and/or one or morethrough silicon vias and/or one or more conductive pillars and/or one ormore solder bumps or balls and/or a ball grid array (BGA). In someembodiments, an ultrasound-on-a-chip may be bonded to a substrate viaflip-chip bonding.

The aspects and embodiments described above, as well as additionalaspects and embodiments, are described further below. These aspectsand/or embodiments may be used individually, all together, or in anycombination of two or more, as the application is not limited in thisrespect.

I. EDGE-CONTACT VIAS

Some embodiments relate to vertical integrated interconnects includingedge-contact vias. Edge-contact vias may provide access to ultrasoundtransducers through the bottom surface of an ultrasound-on-a-chip (theinterface surface between an ultrasound-on-a-chip and the substrate onwhich the ultrasound-on-a-chip is disposed). Formation of edge-contactvias of the types described herein may involve formation of a trenchthrough the interface surface of an ultrasound-on-a-chip and formationof one or more vias in the trench.

FIG. 2A is a cross-sectional view of an ultrasound chip comprisingedge-contact vias, according to some non-limiting embodiments.Ultrasound chip 200 includes an ultrasound transducer substrate 201 anda circuit substrate 202. These substrates may be bonded to one anotherin any suitable way. Ultrasound transducer substrate 201 includes aplurality of ultrasound transducers and circuit substrate 202 includescircuits, such as complementary metal-oxide-semiconductor (CMOS)circuits, for controlling the operations of the ultrasound transducers.In some embodiments, ultrasound transducer substrate 201 includescapacitive micromachined ultrasound transducers (CMUTs), though othertypes of transducers may be used including piezoelectric MUTs (PMUTs).

The ultrasound transducers include a sealed cavity 210 formed between amembrane 212 and a bottom electrode 230. The combination of sealedcavity 210, membrane 212 and bottom electrode 230 may form a CMUT. Thecavities 210 may be formed by bonding ultrasound transducer substrate201 and circuit substrate 202 together. Membrane 212 may serve as thetop electrode. In some embodiments, one or more of membrane 212 andbottom electrode 230 may include silicon. In some such embodiments, tofacilitate operation as of the CMUT, membrane 212 and bottom electrode230 may be doped to act as conductors, and in some cases may be highlydoped (e.g., having a doping concentration greater than 10¹⁵ dopants/cm³or greater). When a time-varying voltage is applied between membrane 212and bottom electrode 230, the membrane vibrates thus producing acoustic(e.g., ultrasound) waves. Additionally, when an acoustic wave hits anultrasound transducer, a voltage arises between membrane 212 and bottomelectrode 230. Accordingly, the combination of cavity 210, membrane 212and bottom electrode 230 forms an ultrasound transducer.

Ultrasound chip 200 is designed to provide electric access from outsidethe chip to the bottom electrodes 230 and membranes 212 usingedge-contact vias 222. The cross-sectional view of FIG. 2A illustratestwo edge-contact vias, though any other suitable number of vias may bepresent. Each edge-contact via 222 is formed inside a trench 220, whichin turn is formed in the handle (203) of circuit substrate 202. Thefirst edge-contact via 222 of FIG. 2A (positioned on the left-hand sideof ultrasound chip 200) provides electric access to a membrane 212. Morespecifically, this edge-contact via 222 electrically couples a bond pad250 (formed at interface surface 205) with a pad 224. Pad 224 is coupledto a membrane 212 via conductive structure 226, which include one ormore conductive portions extending parallel to the z-axis. Bond pad 250may be placed in electrical contact with a corresponding pad formed onan underlying substrate on which ultrasound chip 200 is mounted. Forexample, conductive pads 250 may connected to a BGA, solder bumps,solder balls, or other surface mounting interconnects.

The second edge-contact via 222 of FIG. 2A (positioned on the right-handside of ultrasound chip 200) provides electric access to bottomelectrode 230. More specifically, this edge-contact via 222 electricallycouples a bond pad 250 with a bottom electrode 230.

As shown in FIG. 2A, edge-contact vias 222 extend primarily in adirection that is angled with respect to interface surface 205. In thisexample, edge-contact via 222 extends in the vertical direction(parallel to the z-axis). Each edge-contact via 222 may be smaller (inthe lateral direction and/or the vertical direction) of the trench 220in which the via is formed. In some embodiments, a trench 220 mayinclude more than one edge-contact via, as illustrated in FIG. 2B, abottom view of ultrasound chip 200 at interface surface 205. This trench220 includes six edge-contact vias 222 (though other trenches mayinclude any other suitable number of vias). The edge-contact vias 222may be spaced from one another in a direction parallel to the y-axis insome embodiments, or may be arranged in any other configuration. Eachedge-contact via couples a bond pad 250 with a corresponding membrane212, or a bond pad 250 with a corresponding bottom electrode 230. Inthis example, each bond pad 250 is connected to a solder bump 260 forenabling electrical contact with an underlying substrate.

FIGS. 3A-3F illustrate a fabrication sequence for fabricating anedge-contact via, in accordance with some non-limiting embodiments. Atthe process step of FIG. 3A, a trench 220 is formed through the handle203 and, subsequently, an opening 221 is formed inside trench 220. Theopening 221 may uncover the bottom surface of a pad 224 (or the bottomsurface of a bottom electrode 230). Trench 220 and opening 221 may beformed using any suitable type of etching technique, including forexample reactive ion etching (RIE). In some embodiments, more than onevia may be formed for each trench. The depth (along the z-axis) of atrench 220 may be, among other possible values, between 50 μm and 500μm, between 50 μm and 300 μm, between 50 μm and 200 μm, or between 50 μmand 150 μm. The width (along the x-axis or the y-axis) of a trench 220may be, among other possible values, between 100 μm, and 500 μm, between100 μm and 300 μm, between 200 μm and 400 μm or between 250 μm and 350μm.

At the process step FIG. 3B, the inner walls of trench 220 and opening221 are lined with a layer of insulative material 240. The insulativematerial may include epoxy and/or silicon oxide in some embodiments. Forexample, a silicon oxide may be first deposited, and then a layer ofepoxy may be deposited on the silicon oxide layer. The layer ofinsulative material may be included to increase electrical isolationbetween the resulting edge-contact via and handle 203. As a result, Theedge-contact via may be able to withstand high voltages, thus enablinghigh voltage operation. For example, the edge-contact via may be able towithstand voltages in excess of 25V, 50V, or 100V, among other possiblevalues.

At the process step of FIG. 3C, an opening 242 is formed throughinsulative material layer 240, thus uncovering the bottom surface of pad224 (or the bottom surface of bottom electrode 230).

At the process step of FIG. 3D, a layer of conductive material 244 isdeposited on the insulative material layer 240. Conductive material 244may be deposited on the inner walls of trench 220 and partially on thebottom surface of handle 203. Conductive material 244 may be inelectrical contact with the bottom surface of pad 224 (or the bottomsurface of bottom electrode 230). Conductive material 244 may be formedof aluminum, copper, or any other suitable metallization material.Optionally, a passivation layer 246 may be deposited on conductivematerial 244 (see FIG. 3E). A portion of the passivation layer 246 maybe removed in correspondence with the conductive material on the bottomsurface of handle 203, thus opening a bond pad 250.

At the process step of FIG. 3F, ultrasound chip 200 is surface mountedto a substrate 270. Surface mounting may include flip-chip bonding insome embodiments. For example, ultrasound chip 200 may be mounted suchthat a solder bump 260 (or solder ball) is connected between a bond pad250 and a corresponding solder bump 271 (or solder ball) formed on thetop surface of substrate 270. Ball grid arrays may be used in someembodiments to provide connection.

Substrate 270 may include any suitable type of substrate, including aninterposer (e.g., a silicon interposer) or a printed circuit board. Insome embodiments, ultrasound chip 200 is mounted on an interposer, andthe resulting assembly is mounted on a printed circuit board. One sucharrangement is illustrated in FIG. 4, in accordance with somenon-limiting embodiments. As shown in this figure, ultrasound chip 200may be surface mounted to substrate 270 (an interposer in this case),with solder bump 260 being connected to solder bump 271. The surfacemounted assembly may be mounted to printed circuit board 280, withsolder bump 274 being connected to solder bump 282. Substrate 270 mayinclude in-plane conductive traces (not shown in FIG. 4) for routingelectric signals as desired. Additionally, substrate 270 includes vias,such as via 272, for allowing transfer of electric signals betweenprinted circuit board 280 and ultrasound chip 200. In some embodiments,printed circuit board 280 includes other electronic devices (not shownin FIG. 4), such as one or more digital chips for processing theinformation obtained using the ultrasound transducers, and optionallyfor compressing the information.

Ultrasound chip 200 may have a width (w3) between 100 μm and 1 cm,between 100 μm and 7.5 mm, between 100 μm and 5 mm, between 100 μm and2.5 mm or between 100 μm and 1 mm, or any other suitable range withinsuch ranges. Other ranges are also possible. Ultrasound chip 200 mayhave a thickness (t3) between 100 μm and 1 cm, between 100 μm and 7.5mm, between 100 μm and 5 mm, between 100 μm and 2.5 mm, between 100 μmand 1 mm, between 100 μm and 750 μm, between 100 μm and 500 μm, between100 μm and 300 μm, or any other suitable range within such ranges.

II. THROUGH SILICON VIAS

Some embodiments relate to vertical integrated interconnects includingthrough silicon vias (TSV). Similar to edge-contact vias, throughsilicon vias provide access to the ultrasound transducers through thebottom surface of the ultrasound-on-a-chip.

An example of an ultrasound chip including through silicon vias isillustrated in FIG. 5, in accordance with some non-limiting embodiments.Ultrasound chip 500 includes an ultrasound transducer substrate 501bonded to a circuit substrate 502, such as a CMOS substrate. Theultrasound transducer substrate 501 includes a plurality of cavities510, a first silicon device layer 518, a second silicon device layer512, a silicon oxide layer 526, a passivation layer 514 and siliconoxide portions 516. The cavities 510 are formed between the firstsilicon device layer 518 and the second silicon device layer 512. Thesilicon oxide layer 526 (e.g., a thermal silicon oxide such as a siliconoxide formed by thermal oxidation of silicon) is formed between thefirst and second silicon device layers 518 and 512, with the cavities510 being formed therein. The silicon oxide portions 516 may representthe silicon oxide layer on one substrate that was bonded to the siliconoxide layer 526 that was on the other substrate prior to bonding. Inthis non-limiting example, the first silicon device layer 518 may serveas a bottom electrode and the second silicon device layer 512 may beconfigured as a membrane. Thus, the combination of the first silicondevice layer 518, the second silicon device layer 512, and the cavities510 may form ultrasound transducers (e.g., CMUTs), of which six areillustrated in this non-limiting cross-sectional view. To facilitateoperation as a bottom electrode or membrane, one or both of the firstsilicon device layer 518 and second silicon device layer 512 may bedoped to act as conductors, and in some cases may be highly doped (e.g.,having a doping concentration greater than 10¹⁵ dopants/cm³ or greater).The passivation layer 514 passivates the first silicon device layer 518.The top surface 511 of the ultrasound-on-a-chip represents the face fromwhich ultrasound energy will be transmitted by the ultrasoundtransducers for imaging. Therefore, the top face 511 represents thesensor face of the ultrasound device of which the ultrasound chip 500 isa part.

The circuit substrate 502 includes metallization 534, an insulativelayer 528, a bulk silicon layer 503, through-silicon vias (TSVs) 520,and solder bumps 560. The metallization 534 may be formed of aluminum,copper, or any other suitable metallization material, and may representat least part of an integrated circuit formed in the circuit substrate502. For example, the metallization 534 may serve as a routing layer,may be patterned to form one or more electrodes, or may be used forother functions. In practice, the circuit substrate 502 may include morethan one metallization layer, but for simplicity only one metallization534 is illustrated.

TSVs 520 are vias that pass through the handle 503 of circuit substrate502 and extend in the vertical direction. The TSVs 520 may transmitelectrical signals between one or more integrated circuits included inthe circuit substrate 502 and the solder bumps 560, which are oninterface surface 505 (the bottom surface) of ultrasound chip 500. TheTSVs 520 may be formed for example, from copper, doped silicon, dopedpolysilicon, or tungsten. (Electrical connection between the TSVs 520and integrated circuits in the integrated circuit substrate 502 are notshown in FIG. 5). The ultrasound chip 500 further includes bondingstructures 532 and a passivation layer 536 formed in preparation forforming the bonding structures 532. The bonding structures 532electrically connect the ultrasound transducer substrate 501 to thecircuit substrate 502. Accordingly, electrical signals may betransmitted from the integrated circuit substrate 502, through thebonding structures 532, and to the ultrasound transducer substrate 501,and vice versa.

Ultrasound chip 500 may have a width (w4) between 100 μm and 1 cm,between 100 μm and 7.5 mm, between 100 μm and 5 mm, between 100 μm and2.5 mm or between 100 μm and 1 mm, or any other suitable range withinsuch ranges. Other ranges are also possible. Ultrasound chip 200 mayhave a thickness (t4) between 100 μm and 1 mm, between 100 μm and 750μm, between 100 μm and 500 μm, between 100 μm and 300 μm, between 100 μmand 200 μm, or any other suitable range within such ranges.

Ultrasound chip 500 may be surface mounted to any suitable substrate,such as an interposer or a printed circuit board. In some embodiments,ultrasound chip 500 is mounted on an interposer (e.g., a siliconinterposer), and the resulting assembly is mounted on a printed circuitboard. One such arrangement is illustrated in FIG. 6, in accordance withsome non-limiting embodiments. In this example, ultrasound chip 500 maybe surface mounted to substrate 270 (an interposer in this case), withsolder bump 560 being connected to solder bump 271. The surface mountedassembly may be mounted to printed circuit board 280, with solder bump274 being connected to solder bump 282.

FIGS. 7A-7F illustrate a fabrication sequence for fabricating anultrasound chip with TSVs, in accordance with some non-limitingembodiments. Ultrasound chip 500 may be fabricated using the sequence ofFIGS. 7A-7F or using any other suitable fabrication sequence.

At the process step of FIG. 7A, a circuit substrate 502 having circuitsformed therein is provided, and a region of circuit substrate 502 isdoped via ion implantation. Subsequently, as shown in FIG. 7B, the dopedregion (or at least a portion of the doped region) may be etched to forma column (544) of doped silicon. When formed, doped silicon column 554is surrounded by a recess, which in some embodiments is shaped as aring. Doped silicon column 554 may serve as TSV 520 of FIG. 5.Subsequently, as shown in FIG. 7C, the recess may be filled with aninsulative material 556, such as silicon oxide.

At the process step of FIG. 7D, circuit substrate 502 is bonded toultrasound transducer substrate 501. Doped silicon columns 554 mayprovide access to first silicon device layer 518 and second silicondevice layer 512. At the process step of FIG. 7E, grinding may beperformed on the handle 503 of circuit substrate 502. The result is asubstantial reduction in the thickness of the chip. In some embodiments,more than half of the original handle thickness may be removed bygrinding. The resulting chip may have a thickness between 100 μm and 300μm in some embodiments. After grinding, the bottom side of doped siliconcolumns 554 may be exposed, thus enabling access to the doped siliconcolumns 554 from the bottom surface of the chip.

At the process step of FIG. 7F, the chip is surface mounted to asubstrate 270. Surface mounting may include flip-chip bonding in someembodiments. For example, the chip may be mounted such that a solderbump 560 (or solder ball) connects a doped silicon column 544 with acorresponding solder bump 271 (or solder ball) formed on the top surfaceof substrate 270. Ball grid arrays may be used in some embodiments toprovide connection.

III. CONDUCTIVE PILLARS

Some embodiments relate to vertical integrated interconnects includingconductive pillars. Conductive pillars of the types described hereinprovide access to ultrasound transducers through the top surface of anultrasound chip (the surface opposite the mounting surface).

An example of an ultrasound chip including conductive pillars isillustrated in FIG. 8, in accordance with some embodiments. Ultrasoundchip 800 includes an ultrasound transducer substrate 801, a circuitsubstrate 802, a handle substrate 870 and a conductive pillar 822(embedded within support 820). Ultrasound transducer substrate 801 andcircuit substrate 802 may have characteristics similar to those ofultrasound transducer substrate 201 and circuit substrate 202, asdescribed in connection with FIG. 2A. For example, cavity 810, membrane812, bottom electrode 830 and conductive structure 826 may havecharacteristics similar to those of cavity 210, membrane 212, bottomelectrode 230 and conductive structure 226, respectively. Circuitsubstrate 802 is mounted on handle substrate 870, which may be made ofany suitable dielectric material, including for example polyimide.Solder bumps 874 (or other types of interconnects) may connect thebottom surface of handle substrate 870 to an underlying interposer orprinted circuit board.

Electric access to the ultrasound transducers is provided via conductivepillars 822. FIG. 8 illustrates a chip with a single conductive pillar.However, multiple conductive pillars may be used to enable independentcontrol of different ultrasound transducers. The conductive pillars maybe disposed near the outer perimeter of ultrasound transducer substrate801. To provide mechanical support, conductive pillar 822 is embeddedwithin support 820 in some embodiments. Support 820 may bonded to handlesubstrate 870 in any suitable manner, and includes a portion extendingprimarily in the vertical direction. Handle substrate 870 includes ametal layer 840 for providing electrically connection between solderbump 874 and conductive pillar 822 when support 820 is mounted to handlesubstrate 870.

Conductive pillar 822 may include copper in some embodiments. In somesuch embodiments, the conductive pillar is a copper pillar. However,other materials may be used for the conductive pillar, including forexample aluminum and tungsten. Conductive pillar 822 extends primarilyin the vertical direction.

Support 820 may include an insulative material 818, such as epoxy,polyimide and/or silicon oxide. Insulative material 818 separatesconductive pillar 822 from substrates 801 and 802 in-plane. Theseparation (s) may be sufficiently large to enable high voltageoperations. Such separations, in fact, may increase the electricisolation between conductive pillar 822 and substrates 801 and 802. Forexample, separation s may be between 100 μm and 1 mm, between 100 μm and750 μm, between 100 μm and 500 μm, or between 100 μm and 250 μm, amongother possible values. As a result, conductive pillar 822 may be able towithstand voltages in excess of 50V, 75V, 100V or 125V withoutexperiencing electric breakdown.

Support 820 may further support conductive layer 840, which may includecopper, or aluminum, among other possible conductors. Conductive layer840 may be patterned to form conductive traces that extend in a planeparallel to the xy-plane. The plane of conductive layer 840 lies abovethe top surface of ultrasound transducer 801 in some embodiments. Toprovide contact with membrane 812 or bottom electrode 830, a verticalconnection 842 may be provided. Vertical connection 842 may be supportedby support 820 and may extend from the plane of the conductive trace 840in the downward direction parallel to z-axis. In the example of FIG. 8,vertical connection 842 connects to conductive structure 826, which inturn connects to a bottom electrode 830. Similar arrangements, notillustrated in FIG. 8, may be used to contact a membrane 812.

In some embodiments, ultrasound chip 800 includes more than oneconductive layer 840. The different conductive layers may be atdifferent planes along the z-axis. In these embodiments, having multipleplanes of conductive layers may simplify the routing between theconductive pillars and the respective ultrasound transducers.

V. CONCLUSION

Aspects of the technology described herein may provide one or morebenefits, some of which have been previously described. Now describedare some examples of such benefits. It should be appreciated that notall aspects and embodiments necessarily provide all of the benefits nowdescribed. Further, it should be appreciated that aspects of thetechnology described herein may provide additional benefits to those nowdescribed.

Some aspects of the technology described herein provide verticalpackaging techniques for ultrasounds-on-a-chip that do not resort towire bonding. As a result, ultrasound-on-a-chip that employ suchpackaging techniques are substantially narrower and/or substantiallythinner than other types of ultrasound-on-a-chip. The width reductionmay enable probing of small features.

Some aspects of the technology described herein provideultrasounds-on-a-chip that are substantially less power hungry thanultrasound chips using bond wires. This is because the integratedinterconnects used in such ultrasounds-on-a-chip are shorter than bondwires, and as a result, have less inductance. The power reduction mayenable use of these ultrasounds-on-a-chip is low-power applications.

Some aspects of the technology described herein provideultrasounds-on-a-chip that can withstand high voltages, such as inexcess of 100V in some embodiments. The ability to withstand such highvoltages may be achieved thanks to the presence of insulative layersbetween the circuit substrate and the integrated interconnects.

Various aspects of the present disclosure may be used alone, incombination, or in a variety of arrangements not specifically discussedin the embodiments described in the foregoing and is therefore notlimited in its application to the details and arrangement of componentsset forth in the foregoing description or illustrated in the drawings.For example, aspects described in one embodiment may be combined in anymanner with aspects described in other embodiments.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Multiple elements listed with“and/or” should be construed in the same fashion, i.e., “one or more” ofthe elements so conjoined. Other elements may optionally be presentother than the elements specifically identified by the “and/or” clause,whether related or unrelated to those elements specifically identified.Thus, as a non-limiting example, a reference to “A and/or B”, when usedin conjunction with open-ended language such as “comprising” can refer,in one embodiment, to A only (optionally including elements other thanB); in another embodiment, to B only (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

Use of ordinal terms such as “first,” “second,” “third,” etc., in theclaims to modify a claim element does not by itself connote anypriority, precedence, or order of one claim element over another or thetemporal order in which acts of a method are performed, but are usedmerely as labels to distinguish one claim element having a certain namefrom another element having a same name (but for use of the ordinalterm) to distinguish the claim elements.

As used herein, reference to a numerical value being between twoendpoints should be understood to encompass the situation in which thenumerical value can assume either of the endpoints. For example, statingthat a characteristic has a value between A and B, or betweenapproximately A and B, should be understood to mean that the indicatedrange is inclusive of the endpoints A and B unless otherwise noted.

The terms “approximately” and “about” may be used to mean within ±20% ofa target value in some embodiments, within ±10% of a target value insome embodiments, within ±5% of a target value in some embodiments, andyet within ±2% of a target value in some embodiments. The terms“approximately” and “about” may include the target value.

Also, the phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having,” “containing,” “involving,” andvariations thereof herein, is meant to encompass the items listedthereafter and equivalents thereof as well as additional items.

Having described above several aspects of at least one embodiment, it isto be appreciated various alterations, modifications, and improvementswill readily occur to those skilled in the art. Such alterations,modifications, and improvements are intended to be object of thisdisclosure. Accordingly, the foregoing description and drawings are byway of example only.

What is claimed is:
 1. A device comprising: an ultrasound-on-a-chipcomprising one or more ultrasound transducers, wherein theultrasound-on-a-chip has a first surface that is mounted to a substrateand a second surface opposite the first surface; and a first integratedinterconnect that electrically connects the substrate to the one or moreultrasound transducers, wherein the first integrated interconnectcomprises a conductive pillar that extends, continuously, from the firstsurface to the second surface such that the first surface iselectrically connected to the one or more ultrasound transducers throughthe second surface, and the first integrated interconnect is spaced fromthe ultrasound-on-a-chip in a direction substantially parallel to thefirst surface.
 2. The device of claim 1, further comprising a metalportion electrically connecting the first integrated interconnect to thesubstrate.
 3. The device of claim 1, wherein the first integratedinterconnect further comprises a conductive layer coupled to theconductive pillar and extending in the direction substantially parallelto the first surface.
 4. The device of claim 1, wherein theultrasound-on-a-chip further comprises a conductive portion electricallyconnecting the first integrated interconnect with a bottom electrode ofthe one or more ultrasound transducers.
 5. The device of claim 1,wherein the conductive pillar is embedded within an insulative supportthat is coupled to the ultrasound-on-a-chip.
 6. The device of claim 1,wherein the one or more ultrasound transducers each comprise: A bottomelectrode electrically connected to the first integrated interconnect; amembrane; and one or more cavities formed between the bottom electrodeand the membrane.
 7. The device of claim 6, wherein theultrasound-on-a-chip comprises a plurality of the ultrasoundtransducers, and in each of the ultrasound transducers, a plurality ofthe cavities is formed between the bottom electrode and the membrane. 8.The device of claim 6, wherein the membrane is electrically connected toa second integrated interconnect, and the first integrated interconnectis electrically isolated from the second integrated interconnect.
 9. Thedevice of claim 1, wherein the conductive pillar has a height less than1.5 mm.
 10. The device of claim 1, wherein the conductive pillar has aheight less than 1 mm.
 11. The device of claim 1, wherein the conductivepillar has a height greater than a height of the ultrasound-on-a-chip.12. The device of claim 1, wherein a second integrated interconnectelectrically connects the substrate to the one or more ultrasoundtransducers, and the first integrated interconnect is electricallyisolated from the second integrated interconnect.
 13. The device ofclaim 1, wherein the second integrated interconnect comprises aconductive pillar that extends, continuously, from the first surface tothe second surface such that the first surface is electrically connectedto the one or more ultrasound transducers through the second surface.14. The device of claim 1, wherein the spacing between the firstintegrated interconnect and the ultrasound-on-a-chip is greater than orequal to 100 micrometers.
 15. An ultrasound device, comprising: anultrasound-on-a-chip comprising one or more ultrasound transducers,wherein the ultrasound-on-a-chip has a first surface that is mounted toa substrate and a second surface opposite the first surface; aninterposer spaced from the ultrasound-on-a-chip in a first direction;and a first integrated interconnect that electrically connects theinterposer to the one or more ultrasound transducers, the firstintegrated interconnect comprising a conductive pillar spaced from theultrasound-on-a-chip in a second direction perpendicular to the firstdirection, wherein the conductive pillar extends, continuously, from thefirst surface to the second surface such that the first surface iselectrically connected to the one or more ultrasound transducers throughthe second surface.
 16. The ultrasound device of claim 15, wherein awidth of the ultrasound device along the second direction is less than30 mm.
 17. The ultrasound device of claim 15, wherein the conductivepillar has a height along the first direction greater than a height ofthe ultrasound-on-a-chip along the first direction.
 18. The device ofclaim 15, wherein, a second integrated interconnect electricallyconnects the substrate to the one or more ultrasound transducers, andthe first integrated interconnect is electrically isolated from thesecond integrated interconnect.
 19. The device of claim 15, wherein thesecond integrated interconnect comprises a conductive pillar thatextends, continuously, from the first surface to the second surface suchthat the first surface is electrically connected to the one or moreultrasound transducers through the second surface.
 20. The device ofclaim 15, wherein the spacing between the first integrated interconnectand the ultrasound-on-a-chip is greater than or equal to 100micrometers.